Monolithic Power Systems, Inc.
MX ˙ BMV ˙ US6098391054
SecurityMX:MPWR / Monolithic Power Systems, Inc.
InstitutionRathbone Brothers plc
Latest Disclosed Ownership4,929 shares
Latest Disclosed Value $ 5,389,122
Rathbone Brothers plc reports 10.95% decrease in ownership of MPWR / Monolithic Power Systems, Inc.

On May 12, 2026 - Rathbone Brothers plc filed a 13F-HR form disclosing ownership of 4,929 shares of Monolithic Power Systems, Inc. (MX:MPWR) valued at $5,389,122 USD as of March 31, 2026. The entity filed a previous 13F-HR/A on February 6, 2026 disclosing 5,535 shares of Monolithic Power Systems, Inc.. This represents a change in shares of -10.95% during the quarter.

Institutional Ownership: 13F and NPORT Filings

The Security and Class in the table below are shown exactly as filed by the investor. We do our best to track continuity of investments through acquisitions, and this will be reflected in the table as changes in names. In addition to descriptive data, performance of the investment is shown over time. To calculate quarterly performance, we first calculate cost basis of the shares purchased during the quarter, then use that to calculate gross profit. Quarterly return is Gross Profit / Starting Portfolio value.

Note that cost basis is calculated and stored in thousands, so small quarterly changes in shares frequently result in a cost basis of zero.

Upgrade to unlock premium data and export to Excel .

Disclosed Equity Positions (from 13F/NPORT Filings)
File
Date		 Effective
Date		Form Security Class ID Avg Price
Paid (Est)		 Reported
Shares		 ΔShares ΔShares
(%)		 Reported
Value
(x1000)		 ΔValue
(%)		 Alloc
(%)		 ΔAlloc ΔAlloc (%) Cost Basis
(x1000)		 Unrealized
Gain/Loss
(x1000)
2026-05-12 2026-03-31 13F MONOLITHIC POWER SYSTEM INC USD0.001 COM 609839105 4,929 -606 -10.95 5,389 7.44 0.0230
2026-02-06 2025-12-31 13F/A-1 MONOLITHIC POWER SYSTEM INC USD0.001 COM 609839105 5,535 -140 -2.47 5,017 -3.98 0.0199
2026-01-21 2025-12-31 13F MONOLITHIC POWER SYSTEM INC USD0.001 COM 609839105 5,535 -140 5,017 0.0199
2025-11-13 2025-09-30 13F MONOLITHIC POWER SYSTEM INC USD0.001 COM 609839105 5,675 -25 -0.44 5,225 25.34 0.0212
2025-08-07 2025-06-30 13F MONOLITHIC POWER SYSTEM INC USD0.001 COM 609839105 5,700 705 14.11 4,169 43.87 0.0180
2025-05-13 2025-03-31 13F MONOLITHIC POWER SYSTEM INC USD0.001 COM 609839105 4,995 1,488 42.43 2,897 39.61 0.0140
2025-02-13 2024-12-31 13F MONOLITHIC POWER SYSTEM INC USD0.001 COM 609839105 3,507 2,343 201.29 2,075 92.84 0.0100
2024-11-13 2024-09-30 13F MONOLITHIC POWER SYSTEM INC USD0.001 COM 609839105 1,164 48 4.30 1,076 17.47 0.0054
2024-08-09 2024-06-30 13F MONOLITHIC POWER SYSTEM INC USD0.001 COM 609839105 1,116 1,116 917 0.0050
Legend
Shares
The total number of shares held by the institution at the end of the reporting period (the effective date). This is provided in the filing.
Value
The total value of the shares as of the effective date. This is provided in the filing.
Avg. Share Price
The weighted average share price of the shares held by the institution. We use FIFO accounting to determine this price
Class
This is the security class as indicated by the filer. There are a variety of values for this field. Common values include "EC" = equity common, "EP" - equity preferred
Allocation (%)
The percent of the institution's portfolio that this position represents. This is provided in NPORT filings. For 13F filings, we calculate it.
Change in Allocation
The change in allocation from the prior reporting period. This is calculated as current allocation - prior allocation.
Change in Allocation (%)
The percent change in allocation from the prior reporting period. This is calculated as (current allocation - prior allocation) / prior allocation.
Cost Basis
The total cost of the shares held. This is calculated as reported shares * avg. share price
Unrealized Gain/Loss
This is the market value of the position as of the effective date minus the cost basis.