A new AC microcalorimetry set-up, which facilitates scanning the pressure (P) at low temperatures (T) permits the precise determination of the (P, 7) phase diagram of the intermediate valence compound TmSe in a wide pressure range (0-14 GPa). In the low-pressure area, the occurrence of a phase transition at 3 GPa is confirmed. Contrary to previous measurements which indicated a possible new transition at 6 GPa, our results show a continuous behaviour with a Neel temperature increasing linearly with P. Above 10 GPa, the splitting of the magnetic anomaly might indicate a new phase transition. The same kind of experiment was performed for TmS, and after a P shift of 7 GPa, a scaling can be realized between the two compounds.