This paper presents a new method of analysis and measurement. When a semiconductor wafer is illuminated by microwave and light, the microwave transmission coefficient(MTC) through a sample is related to the wavelength of light. When the wavelength of light is continuously changed, the MTC is changed simultaneously. We have theoretically analyzed the relationship among the MTC and the diffusion length, and the lifetime of minority carrier and the surface recombination velocity. All these parameters can be determined by the microwave and light absorption spectroscopy. We made an instrument to measure the MTC at various light wavelengths. This is a contactless measuring method, with a measuring area being circular spot about 7mm2. The sample can be removed freely on the testboard. There is a calculating result with a minimal standard deviation by using a program of nonlinear curve fitting. When a semiconductor wafer is illuminated by microwave and light, the microwave transmission coefficient (MTC) through a sample is related to the wavelength of light. When the wavelength of light is continuously changed, the We have theoretically analyzed the relationship among the MTC and the diffusion length, and the lifetime of minority carrier and the surface recombination velocity. All these parameters can be determined by the microwave and light absorption spectroscopy. We made an instrument to measure the MTC at various light wavelengths. This is a contactless measuring method, with a measuring area being circular spot about 7mm2. The sample can be removed freely on the testboard. There is a calculating result with a minimal standard deviation by using a program of nonlinear curve fitting.