A high speed random bit generator is proposed with chaotic semiconductor laser used as the entropy source. Analogue-to-digital conversion is realized by high frequency electronic devices such as amplifier, comparator, and trigger. One bit sequence is generated and exclusive OR (XOR) operated with other different bit sequences, and data processing in computer is needless. The generator outputs a 500 Mb/s random bit sequence. The obtained sequence passed the statistic test of national institute of standards and technology (NIST, SP800-22). It has the advantages of tunable speed and compact size, which make it easy to become a production.