Abstract: A mushroom gate structure InP MISFET was developed by the electron beam evaporation and chosen chemical etching. The device has n⁺-InP/n-InP/SI-InP:Three layers structure which made by LP-MOCVD as matter, has Ti-Al film as gate electrode, has Ti-Al/Au-Ge film as source electrode or drain electrode. The gate dimension is 0.002mm× 0.2 mm. The D C Character shows that the transconductance gm is about 80~115 ms/mm, the threshold voltage V_T is about -3.62 V, the channel effective electron mobility is about 674 cm²/V·S, the average electron velocity Va is about 1.22× 10⁷ cm/s, the interface state density N_ss is about 9.56× 10¹¹ cm^-2, The cut-off frequency fT is about 97.1GHz, the maximum working frequency f^max is about 64.7GHz. Up to now, we have not fought the flotation of device quality. The device can be used in InP substrate OEIC as amplificatory element.