The specific heat of the ferroelectric–paraelectric phase transition in TGSe under several electric fields in therange 175–750 V cm−1 has been measured and analysed in terms of the same tricriticalLandau potential obtained at zero electric field plus the term−ξQ, which represents the simplest form to include the coupling between the order parameterQ and theelectric field E (). Data in the ferroelectric phase have been successfully fitted and it has been found thatξ = k(E+E0), wherek is constantand E0∼150 V cm−1. It has been found that in order to describe the behaviour in both phases simultaneously itis necessary to consider a more complex coupling between the electric field andthe order parameter, which makes the critical temperature and the coefficient ofQ6 in the tricritical potential be renormalized by the field.