A model to study the annual behaviour of the temperature of a homogeneous solid (considered like a semispace) will be presented in this paper. The model gives the temperature of the solid at any time and at any depth. It assumes the solar flux as the incoming flux, constant atmospheric effects and a simple expression for the outgoing flux. Finally solutions of the soil temperature, when a meteorological transient (box shape) is present, will be shown. The model gives a qualitative behaviour of the soil temperature on a yearly basis and it is like the many experimentally observed behaviours.