We pursue the program of exposing the intrinsic mathematical structure of the “space of proofs” of a logical system [AJ94b]. We study the case of Multiplicative-Additive Linear Logic (MALL). We use tools from Domain theory to develop a semantic notion of proof net for MALL, and prove a Sequentialization Theorem. This work forms part of a continuation of previous joint work with Radha Jagadeesan [AJ94b] and Paul-Andr´e Melli`es [AM99].