Bates_Model

dS = dH + JSdN

where

H is the Heston process described in Heston Model, albeit with its drift adjusted to compensate for the existence of the jumps.

N is a poisson process with a constant intensity λ

J is a random variable representing the relative jump size ΔS/S := (S'-S)/S, where S' is the underlying price right after a jump, is distributed in such a way that the logarithm of the "jump factor" S'/S = 1+J is normally distributed.

Formally: log(1+J) ~ N(μ,δ²)

where N(μ,δ²) denotes the standard normal distribution with mean μ and standard deviation δ. Web reference available here