This paper presents an improved small-signal model and a W-band monolithic low noise amplifier (LNA) using 100 nm InAlAs/InGaAs/InP-based high electron mobility transistors (HEMT) technology.For improving the fitting accuracy of S-parameters in low frequency, the small-signal model takes into account differential resistances of gate-to-source and gate-to-drain diodes, which modeled by resistances Rfsand Rfd.A W-band LNA monolithic millimeter-wave integrated circuit (MMIC) has been designed and fabricated based on this model to verify the feasibility of this model.The amplifier is measured on-wafer with a small-signal peak gain of 14.4 d B at 92.5 GHz and 3-dB bandwidth from 85 to 110 GHz.In addition, the MMIC also exhibits an excellent noise characteristic with the noise figure of 4.1 dB and the associate gain of 13.8 d B at 88 GHz.This MMIC amplifier shows wider 3-dB bandwidth and higher per-stage gain than others results at the similar band.