We demonstrate W-band monolithic microwave integrated circuit (MMIC) amplifiers based on AlInN/GaN high electron mobility transistors (HEMTs) grown on Silicon. Our MMIC process was fully characterized to 110 GHz and a design kit generated to enable circuit design. A fabricated two-stage amplifier with an output device width of 100 mu m shows a saturated output power of 18.3 dBm and a gain of 8.2 dB at 94 GHz with input/output return losses of -10 dB or better from 90 to 100 GHz. A model confirmed by experimental data revealed that the performance is limited by current collapse and that a doubling of output power could be possible by resolving collapse limitations, showing the considerable potential of GaN-on-Si HEMT technology for low-cost millimeter-wave power electronic applications.