The minority carrier diffusion length in the base region of a solar cell is an important factor affecting the conversion efficiency and spectral response of the cell. Conventional methods for the measurement of minority carrier diffusion lengths in semiconductor materials are generally unsuitable for measurements on completed solar cells. This paper describes a simple and direct technique for the measurement of minority carrier diffusion length in solar cells, It has been applied to both single crystalline and polycrystalline silicon solar cells, and the results compared to standard surface photovoltage measurements.