We apply the phase portrait analysis for photon density and carrier density to analyze simulation results obtained from the rate equations for semiconductor lasers. On the two‐dimensional bifurcation diagram of modulation depth and modulation frequency, there are six regions: periodic pulse, continuous oscillation wave, chaos, period doubling of single period, period multiplying of single period, and period doubling of two period. The region of chaos is located below the region of periodic pulse. By properly choosing the modulation frequency, chaotic behavior can be avoided. A normalized two‐dimensional bifurcation diagram defining the periodic pulse region is presented for the purpose of locating the suitable region for modulation of a semiconductor laser.