A method for carbonitriding of a steel part arranged in a chamber comprises first steps and second steps, a carburizing gas being injected into the chamber during the first steps only and a nitriding gas being injected into the chamber during the second steps only, at least one of the second steps being situated between two first steps, the pressure in the chamber during at least one part of said two first steps being maintained at a first value and the pressure in the chamber during at least one part of said second step situated between said two first steps being at a second value that is strictly greater than the first value.