A micromachined 4-channel Coulter counting device is reported to achieve high throughput counting of microparticles. The design, fabrication and testing of this device is presented. Multiplexed detection was implemented by amplitude modulation of signals from individual channels to obtain a single combined response for all four channels, requiring only one set of detection electronics. Testing results using 30μm polystyrene particles demonstrated the throughput of the multiplexed device was improved 300% by simultaneously detecting particles through its parallel 4 channels. The multiplexed detection principle can be extended to a larger number of channels is to further improve the throughput.