A new experimental technique for the measurement of intrinsic parameters of vertical cavity surface emitting lasers is suggested. Using an external cavity with variable reflectivity we measure the internal quantum efficiency of &eegr;i=0.6 and internal losses of &agr;i=10 cm−1in a gain guided AlGaAs/GaAs laser operating at 850 nm. In addition, transparency current ofI0∼0.46×Ithis obtained, in excellent agreement with a direct measurement. ©1995 American Institute of Physics.