This paper presents some preliminary results on the measurement of carrier lifetime of GaAs diodes by the step recovery method. The lifetime of Si recovery diodes with Boron diffused p-n junction has been measured by the reverse recovery and step recovery methods.The results obtained are fairly consistent, indicating that it meets the requirement of the step recovery method sufficiently well. Therefore, it is suggested that the diode lifetime so obtained is equal to the minority carrier lifetime. In this way, the minority carrier lifetime of GaAs diodes with p-n junction has been determined. The lifetime of GaAs diodes with M-S schottry barrier has also been measured. In this case, however, it is suggested from a preliminary analysis that the measured value is not the minority carrier lifetime.