This paper presents a visco-hyperelastic constitutive model to characterize the temperature-dependent mechan-ical deformation of composite materials during thermoforming. The material of interest was a unidirectional or woven fibrous reinforcement filled with a semi-crystalline thermoplastic matrix. Based on the two laws of thermodynamics, the mechanical model was coupled with the heat equation and a crystallization kinetics model. As a result, the viscoelastic effects and exothermicity of the crystallization reaction, characteristic of the presence of the semicrystalline thermoplastic matrix, constituted internal heat sources taken into account by the heat equation. These were the first steps towards establishing a thermo-chemical-mechanical coupling. In order to validate and parameterize the present law, a thermomechanical characterization of in-plane shear was put forward.