The aim of this paper is to establish some sufficient conditions ensuring the existence and uniqueness of positive (Bohr) almost periodic solutions to a class of semilinear evolution equations of the form: u ′ (t) = A(t)u(t)+𝑓 (t, u(t)), t ∈ R. We assume that the family of closed linear operators (A(t)) t∈R on a Banach lattice X satisfies the "Acquistapace-Terreni" conditions, so that the associated evolution family is positive and has an exponential dichotomy on R. The nonlinear term 𝑓 , acting on certain real interpolation spaces, is assumed to be almost periodic only in a weaker sense (i.e., in Stepanov's sense) with respect to t, and Lipschitzian in bounded sets with respect to the second variable. Moreover, we prove a new composition result for Stepanov almost periodic functions by assuming only continuity of 𝑓 with respect to the second variable (see the condition Lemma 1-(ii)). Finally, we provide an application to a system of Lotka-Volterra predator-prey type model with diffusion and time-dependent parameters in a generalized almost periodic environment.