In the recent literature a number of articles have been dedicated to the study of comparative modal constructions (CMCs) in Germanic languages such as English, Dutch and German. However, CMCs are not restricted to the Germanic area. The present paper presents original data from a Romance language, namely French, in which (at least) three CMCs are attested: faire mieux de 'do better of', valoir mieux 'be worth better' and falloir mieux 'must better'. The aim of this paper is twofold. It intends to offer the first linguistic description of CMCs in French. Making use of several corpora, it presents a synchronic structural characterization of CMCs in Modern French, it investigates their diachronic development and describes their semantics. In addition, the paper seeks to define the degree of grammaticalization of French CMCs. This will enable us to specify their status as semi-auxiliaries within the paradigm of French modals.