The ambipolar-diffusion-with-cutoff (ADC) model is extended to estimate the single-event-induced collected charge for multiple transistors for circuits simulation. The proposed improvement in the model includes both parasitic-bipolar and charge-sharing effects for a given technology. Simulation results indicate excellent agreement between the proposed model and published TCAD data for 130, 90, 65, and 40 nm technology nodes. A comparison between ADC and both rectangular parallelepiped (RPP) and integral rectangular parallelepiped (IRPP) models indicates a 2.7 × and 2.5 × lower error in estimating collected charge when compared with TCAD data. The ADC average error was estimated to be 7.1 fC and for the RPP and IRPP about 19.1 fC and 17.5 fC, respectively, across the technologies for particles with the linear energy transfer range from 1 - 30 MeV-cm 2 /mg.