In this work we demonstrate an on-chip multiplexed multichannel resistive pulse sensor (Coulter counter) for high throughput counting of microscale particles. The design, fabrication and testing of this device are presented. The high throughput counting is a result of using multiple parallel microfluidic channels to analyze the sample. Detection is achieved by using frequency division multiplexing; each microchannel is modulated with its own known and unique frequency, a combined measurement is made across a single pair of electrodes, and the measured signal is demodulated to determine the signal across each individual channel. Testing results using 30 µm polystyrene particles demonstrate that the throughput of the multiplexed device gets improved 300% over a single-channel device; this is achieved by simultaneously detecting particles through the device's four parallel channels. In addition, the ac modulation method used in this paper reduces the polarization effect on the microelectrodes, and thereby allows for measurement of the particle sizes with significantly reduced error. The multiplexed detection principle can be extended to a larger number of channels to further improve the throughput, without increasing the external detection electronics.