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.