This work describes a new computational approach for modeling the radiation-induced transient current and charge collection at circuit-level. Our methodology is based on a random-walk process that takes into account both diffusion and drift of radiation-induced minority carriers in a non-constant electric field both in space and time. The model has been successfully coupled either with an internal routine or with SPICE for circuit solving and feedback on the charge-collection process. It is illustrated here for a junction impacted by an ionizing particle and embedded in a CMOS inverter. (C) 2014 Elsevier Ltd. All rights reserved.