While most artificial pancreases rely mainly on diffusive transport of solutes, Reach et al. (1) proposed a U-shaped device which combines diffusive and convective transports to shorten the lag time between insulin release and a rise in blood glucose concentration. This paper presents a mathematical model which predicts well the performance of the U-shaped hybrid artificial pancreas for both square-wave and ramp glucose stimulations. The model uses a novel insulin secretion equation, and a possible inhibition mechanism regulating insulin secretion is also discussed.