This study investigates the organization of the mental lexicon in Spanish as a foreign language in contrast to its structure in Spanish as a native language through semantic networks derived from lexical availability or semantic fluency tasks. To this end, we collected the responses of 75 American learners of Spanish and 75 native speakers in three semantic categories: ‘Animals’, ‘Body Parts’, and ‘Clothing’. Using advanced network analysis tools, we examined the structural properties of the different networks, delving, at the microscopic level, into the factors that determine the centrality of their nodes. Compared to native lexicon networks, L2 networks are less efficiently organised, less interconnected and their communities are more poorly defined. Regarding centrality, the results highlight the influence of different cognitive factors in the configuration of semantic networks in Spanish as L1 and as L2.