Amphastar Pharmaceuticals, Inc. (AMPH) Ownership
AMPH ownership summary
as of October 18, 2026- Institutions
- 68.3% of shares outstanding
- Insiders
- 30.81% of shares outstanding
- Shares outstanding
- 42.5M
- Float
- 31.3M shares available to trade
- Short interest
- 22.57% 4.4M shares short
- Days to cover
- 8.17 short interest down 11.8% vs prior month
- Institutions 68.32%
- Insiders 30.81%
- Other investors 0.86%
AMPH top institutional holders
20 largest| # | Holder | % of shares | Shares | Value | Change | Reported |
|---|---|---|---|---|---|---|
| 1 | BlackRock Inc | 12.28% | 5.2M | $135.2M | −196,409 (−3.6%) | June 30, 2026 |
| 2 | Dimensional Fund Advisors, Inc. | 5.42% | 2.3M | $59.6M | +277,160 (+13.7%) | June 30, 2026 |
| 3 | State Street Corp | 3.86% | 1.6M | $42.5M | +34,611 (+2.2%) | June 30, 2026 |
| 4 | Vanguard Capital Management, LLC | 3.48% | 1.5M | $38.3M | −61,703 (−4.0%) | June 30, 2026 |
| 5 | American Century Companies Inc | 2.77% | 1.2M | $30.4M | +159,088 (+15.6%) | June 30, 2026 |
| 6 | Marshall Wace Asset Management Ltd | 2.51% | 1.1M | $27.6M | +40,682 (+4.0%) | June 30, 2026 |
| 7 | Geode Capital Management, LLC | 2.28% | 970K | $25.1M | −6,810 (−0.7%) | June 30, 2026 |
| 8 | Fuller & Thaler Asset Management Inc | 2.23% | 949K | $24.6M | −445,901 (−32.0%) | June 30, 2026 |
| 9 | D. E. Shaw & Co LP | 2.09% | 887K | $22.9M | +221,506 (+33.3%) | June 30, 2026 |
| 10 | Vanguard Portfolio Management, LLC | 1.90% | 810K | $20.9M | +21,752 (+2.8%) | June 30, 2026 |
| 11 | LSV Asset Management | 1.51% | 642K | $16.6M | −9,700 (−1.5%) | June 30, 2026 |
| 12 | Renaissance Technologies Corp | 1.23% | 525K | $13.6M | −28,800 (−5.2%) | June 30, 2026 |
| 13 | The Goldman Sachs Group Inc | 1.19% | 505K | $13.1M | +175,972 (+53.4%) | June 30, 2026 |
| 14 | Systematic Financial Management LP | 1.03% | 437K | $11.3M | −15,514 (−3.4%) | June 30, 2026 |
| 15 | Morgan Stanley - Brokerage Accounts | 1.02% | 435K | $11.2M | +14,503 (+3.5%) | June 30, 2026 |
| 16 | UBS Group AG | 0.92% | 393K | $10.2M | −27,153 (−6.5%) | June 30, 2026 |
| 17 | HRT FINANCIAL LLC | 0.91% | 388K | $10.0M | +331,349 (+589.8%) | June 30, 2026 |
| 18 | Denali Advisors LLC | 0.88% | 376K | $9.7M | +109,500 (+41.1%) | June 30, 2026 |
| 19 | Northern Trust Corp | 0.87% | 371K | $9.6M | −1,288 (−0.3%) | June 30, 2026 |
| 20 | Bridge City Capital, LLC | 0.80% | 339K | $8.8M | +3,603 (+1.1%) | June 30, 2026 |
Value at the latest close. Change = shares bought or sold in the latest quarterly filing (13F). In the top 20, 11 holders added 1.4M shares and 9 cut 793K.
AMPH top mutual fund and ETF holders
20 largest| # | Holder | % of shares | Shares | Value | Change | Reported |
|---|---|---|---|---|---|---|
| 1 | iShares Core S&P Small-Cap ETF | 4.40% | 1.9M | $48.5M | +483 (+0.0%) | September 30, 2026 |
| 2 | Avantis US Small Cap Value ETF | 3.06% | 1.3M | $33.6M | +4,872 (+0.4%) | September 30, 2026 |
| 3 | Vanguard MStar Total Stk Mkt Idx Invest | 2.48% | 1.1M | $27.3M | — | August 31, 2026 |
| 4 | TD U.S. Capital Reinvestment I | 2.31% | 982K | $25.4M | −51,467 (−5.0%) | December 31, 2025 |
| 5 | FullerThaler Behavioral Sm-Cp Eq R6 | 2.12% | 903K | $23.4M | −526,200 (−36.8%) | June 30, 2026 |
| 6 | iShares Russell 2000 ETF | 1.97% | 839K | $21.7M | −9,664 (−1.1%) | September 30, 2026 |
| 7 | DFA US Small Cap Value I | 1.40% | 596K | $15.4M | — | August 31, 2026 |
| 8 | Fidelity Small Cap Index | 0.83% | 354K | $9.2M | +3,321 (+0.9%) | July 31, 2026 |
| 9 | State Street® SPDR® S&P® PhrmctlsETF | 0.74% | 314K | $8.1M | −3,898 (−1.2%) | September 30, 2026 |
| 10 | DFA US Targeted Value I | 0.73% | 309K | $8.0M | +32,608 (+11.8%) | August 31, 2026 |
| 11 | iShares Russell 2000 Value ETF | 0.72% | 305K | $7.9M | +464 (+0.2%) | September 30, 2026 |
| 12 | State Street SPDR Port S&P 600 Sm CpETF | 0.68% | 289K | $7.5M | — | September 30, 2026 |
| 13 | Vanguard Tax-Managed Small Cap Adm | 0.63% | 269K | $7.0M | — | August 31, 2026 |
| 14 | Dimensional US Small Cap Value ETF | 0.62% | 265K | $6.9M | +184 (+0.1%) | September 24, 2026 |
| 15 | First Trust Small Cap Core AlphaDEX® ETF | 0.52% | 223K | $5.8M | — | September 30, 2026 |
| 16 | Dimensional US Targeted Value ETF | 0.51% | 215K | $5.6M | +55 (+0.0%) | September 30, 2026 |
| 17 | DFA US Small Cap I | 0.49% | 210K | $5.4M | — | August 31, 2026 |
| 18 | Pacer US Small Cap Cash Cows 100 ETF | 0.47% | 199K | $5.1M | +447 (+0.2%) | September 30, 2026 |
| 19 | DFA US Micro Cap I | 0.45% | 192K | $5.0M | +52 (+0.0%) | August 31, 2026 |
| 20 | Vanguard Russell 2000 ETF | 0.44% | 186K | $4.8M | +4,678 (+2.6%) | August 31, 2026 |
Funds report holdings monthly or quarterly; dates differ by fund.
AMPH insider transactions
latest 11| Date | Name | Transaction | Price | Shares | Value |
|---|---|---|---|---|---|
| 2025-12-17 | Rong Zhou | Sell | $26.20 | 9,787 | $256,419 |
| 2025-12-12 | Floyd F Petersen | Sell | $25.92 | 2,426 | $62,882 |
| 2025-12-11 | Floyd F Petersen | Sell | $25.69 | 1,737 | $44,624 |
| 2025-11-25 | Richard K Prins | Sell | $27.10 | 4,179 | $113,251 |
| 2025-11-13 | Floyd F Petersen | Sell | $26.49 | 16,679 | $441,827 |
| 2025-11-03 | Floyd F Petersen | Sell | $25.27 | 500 | $12,635 |
| 2025-10-01 | Floyd F Petersen | Sell | $27.20 | 500 | $13,600 |
| 2025-08-01 | Floyd F Petersen | Sell | $20.83 | 500 | $10,415 |
| 2025-07-02 | Floyd F Petersen | Sell | $23.47 | 500 | $11,735 |
| 2025-06-02 | Floyd F Petersen | Sell | $25.67 | 500 | $12,835 |
| 2025-05-01 | Floyd F Petersen | Sell | $24.08 | 500 | $12,040 |
Reported trades by company officers, directors and other filers (including disclosures by members of Congress where EODHD lists them). "—" where the filing gives no share count.
AMPH shares outstanding
Year-end shares outstanding, adjusted for splits.
Who owns AMPH
Institutional investors own 68.3% of Amphastar Pharmaceuticals's shares and insiders 30.81%. The largest holder is BlackRock Inc with 12.28% of the shares (5.2M), as of June 30, 2026. Among the top 20 institutions, 11 added shares and 9 reduced their stake in the latest filings. Short interest is 22.57% of the float, or 8.17 days of average trading volume. The share count rose 5.6% since 2014.
Related: AMPH analyst forecast, AMPH key metrics. See the AMPH stock overview for the latest quote and news.
AMPH ownership FAQ
Who owns the most Amphastar Pharmaceuticals stock?
The largest shareholders of Amphastar Pharmaceuticals are BlackRock Inc (12.28%), Dimensional Fund Advisors, Inc. (5.42%), State Street Corp (3.86%), Vanguard Capital Management, LLC (3.48%), American Century Companies Inc (2.77%).
What percentage of Amphastar Pharmaceuticals is owned by institutions?
Institutions hold 68.3% of Amphastar Pharmaceuticals's shares outstanding; insiders hold 30.81%.
Which funds own Amphastar Pharmaceuticals?
The largest fund holders of Amphastar Pharmaceuticals are iShares Core S&P Small-Cap ETF (4.40%), Avantis US Small Cap Value ETF (3.06%), Vanguard MStar Total Stk Mkt Idx Invest (2.48%), TD U.S. Capital Reinvestment I (2.31%), FullerThaler Behavioral Sm-Cp Eq R6 (2.12%).
What is Amphastar Pharmaceuticals's short interest?
4.4M shares of Amphastar Pharmaceuticals were sold short, 22.57% of the float; at the average daily volume it would take 8.17 days to cover.
Are insiders buying or selling Amphastar Pharmaceuticals?
Of the latest 11 reported insider transactions in Amphastar Pharmaceuticals (since May 1, 2025), 0 were purchases and 11 were sales.
How many shares of Amphastar Pharmaceuticals are outstanding?
Amphastar Pharmaceuticals has 42.5M shares outstanding, of which 31.3M are in the public float.