Pedro C. Magalhaes, ‘What are (semi)presidential elections about? A case study of the Portuguese 2006 elections’, in Journal of Elections, Public Opinion and Parties, vol. 17, no. 3, pp. 263-291, October 2007.

A little further back, there was also an interesting article on Portugal by Ana Martins, ‘The Portuguese semi-presidential system. About law in the books and law in action’, in European Constitutional Law Review, vol. 2, pp. 81-100, 2006.