The measurement of the diffusion length of minority charge carriers in a semiconductor crystal body is enabled in that the front side and the rear side of the crystal wafer are each respectively brought into contact with an electrolyte in a respective measuring cell and an inhibiting space charge zone is generated at the front side of the wafer. The front side is irradiated with light having a wave length of .lambda.>800 nm and the front side photocurrent I.sub.1 of the minority charge carriers thereby generated is measured. The diffusion length L can be calculated from the photocurrent I.sub.1 with the assistance of a mathematical equation. The topical distribution of the diffusion length L is obtained given point-by-point irradiation and scanning over the crystal wafer. Diffusion lengths of L 800 nm.