A double-scroll chaotic oscillator based true random number generator (TRNG) is designed and fabricated in CMOS 0.18µm process. In order to realize a TRNG suitable for CMOS process, an op-amp based chaotic oscillator is chosen and transistor-level op-amps are designed. Then, a symmetrically dividing method is proposed to exploit the statistics of chaotic signals generated by the oscillator and improve the throughput of random bits. The TRNG core occupies 0.026mm2 and dissipates 1mW. Measurements show that the generated binary bits can pass the SP800-22 test suites and FIPS140-1 standard with a throughput of 20Mbps.