A CMOS charge pump with improved latch-up immunity is provided. The CMOS charge pump includes a blocking transistor that disconnects first and second boost nodes from a bulk node in response to a blocking control signal, such that a bulk voltage can be maintained at a predetermined level or higher. The CMOS charge pump in a power-up period first precharges the bulk voltage before the main pump performs a boosting operation and prevents a latch-up phenomenon.