In this paper, chaotic light generated by optical feedback semiconductor laser is employed as entropy source. The output waveform of chaotic laser is converted into a binary bit stream by an 8-bit ADC. The generated binary sequences are optimized to equalize the ratio of 1 and 0 by the difference between consecutive sampled 8-bit values. Finally a random bit sequence at rates of up to 1 Gbit/s is realized, and the randomness of long bit strings is verified by the NIST Special Publication 800-22 tests.