Microwave cavity perturbation technique has been employed for the study of photo conductive transients in semiconductors. A new approach of measuring the quality factor of the microwave cavity using cavity perturbation technique (reported in Rev. Sci. Instrum. 65 (1994) 453] is incorporated for this purpose. Measurements with this contactless technique on carrier lifetimes in various single and polysilicon and the analysis of the observed microwave transient photo conductivity decay with temperature is reported.