The minor carrier lifetime of InGaAs(100) after treatment with (NH4)2S solution was measured by the microwave photoconductivity decay (μ-PCD). The result shows that SRV of the InGaAs after treatment with (NH4)2S solution approach that of the nearly ideal InP/InGaAs interface. For better evaluating effect of sulfur, SiNx is deposited on surface of the InGaAs for fabricating MIS. Through measuring the CV properties, the statement of interface is confirmed.