An experimental study of power dropouts in the main mode of a nearly-single-longitudinal-mode GaAlAs semiconductor laser is presented. Knowledge of the statistics of main-mode power dropout interarrival times, depths, and widths is necessary to estimate the performance of a communication system using such laser diodes. We found that at a typical laser operating bias (

), the mean dropout width was 1.8 ns, dropout depths were exponentially distributed, and dropouts falling below 90 percent of the average main-mode power occurred at a rate of

s
-1. Also, the rate of dropouts falling below 90 percent of the average main-mode power was found to increase substantially near mode hops, sometimes by several orders of magnitude.