This paper proposes a novel waveform multiplexing method to realize high channel-density front-end application specific integrated circuit (ASIC) design. In the proposed method, multiplexing is achieved through connecting multiple preamplifiers to a single analog-to-digital converter (ADC). These preamplifiers have different decay time (90%-10%) which will be used as the tag information. The channel information can be identified by analyzing the decay time using digital signal processing. Based on this method, two prototype ASICs have been designed with 2-to-1 multiplexing. They are a 36-channel multiplexing charge sensitive preamplifier ASIC (MCSP) and a 24-channel multiplexing waveform sampling front-end ASIC (MWSFE).