We propose criteria for recess etching to fabricate T-gate used in InGaAs HEMTs. By patterning additional rectangular pads on the source and drain metals in the e-beam lithography step, it is possible to measure the drain-to-source resistance (R_ds) and current (I_ds). the ratio (Γ) of before and after etching for each R_ds and I_ds can be used as criteria to determine the point in time to stop etching. By performing recess etching with Γ= 1.97 for R_ds and Γ= 0.38 for I_ds on an epiwafer having cap doping concentration of 2= 10¹⁹ cm⁻³ and channel indium content of 0.7, we have fabricated InGaAs mHEMT device showing g_m,max= 1603 mS/mm and f_t= 290 GHz at L_g= 124 nm. The criteria presented can be applied to InGaAs HEMTs with various epitaxial structures.