It should typically drop less than 10mV at 150mA with 5V drive, so you should troubleshoot this.

1. Are you sure of the part number (and that it is a genuine part)

2. Check that the gate-source voktage is as-expected

3. Check that the supply voltage is not drooping

It should typically drop less than 10mV at 150mA with 5V drive, so you should troubleshoot this.

1. Are you sure of the part number (and that it is a genuine part)

2. Check that the gate-source voltage is as-expected

3. Check that the supply voltage is not drooping