A method of controlling a gas turbine power plant including a gas turbine engine, and an electric power generator mechanically connected to the gas turbine engine, the gas turbine engine comprising a compressor, a combustor assembly and a turbine; the method comprising determining at least one of a fuel supply and an air supply to the combustor assembly to control at least one of a load (P E) and an exhaust temperature (T E) of the gas turbine engine in accordance with a sliding-mode control technique; the method being further characterized in that controlling comprises determining a sliding quantity (S; S L; S TE), as a function of a control error between a current value and a reference value of a controlled variable, the controlled variable including at least one of a load (P E) and an exhaust temperature (T E) of the gas turbine engine, and determining a control law (U(S, t); U L (S L, t); U TE (S TE, t)), having a gain factor (k(S, t); k L (S L, t); k TE (S TE, t)) and a sliding factor (SF(S, t); SF L (S L, t); SF TE (S TE, t)) and configured to bring the sliding quantity (S; S L; S TE) on a sliding manifold (S') defined by states that cause the sliding quantity (S; S L; S TE) to be zero; the sliding factor (SF(S, t); SF L (S L, t); SF TE (S TE, t)) is a first function of the sliding quantity (S; S L; S TE) and a time derivative ( k̇ ( S,t); k̇ ( S L, t); k̇ ( S TE,t)) of the gain factor (k(S, t); k L (S L, t); k TE (S TE, t)) is a second function of the sliding quantity (S; S L; S TE; and the time derivative ( k̇ ( S, t); k̇ ( S L, t); k̇ ( S TE,t)) of the gain factor (k(S, t); k L (S L, t); k TE (S TE, t)) is negative in a first region (B 1) around the sliding manifold (S'), is zero in a second region (B 2) that surrounds the first region (B 1) and is positive in a third region (B 3) that surrounds the second region (B 2). the method comprising determining at least one of a fuel supply and an air supply to the combustor assembly to control at least one of a load (P E) and an exhaust temperature (T E) of the gas turbine engine in accordance with a sliding-mode control technique; the method being further characterized in that controlling comprises determining a sliding quantity (S; S L; S TE), as a function of a control error between a current value and a reference value of a controlled variable, the controlled variable including at least one of a load (P E) and an exhaust temperature (T E) of the gas turbine engine, and determining a control law (U(S, t); U L (S L, t); U TE (S TE, t)), having a gain factor (k(S, t); k L (S L, t); k TE (S TE, t)) and a sliding factor (SF(S, t); SF L (S L, t); SF TE (S TE, t)) and configured to bring the sliding quantity (S; S L; S TE) on a sliding manifold (S') defined by states that cause the sliding quantity (S; S L; S TE) to be zero; the sliding factor (SF(S, t); SF L (S L, t); SF TE (S TE, t)) is a first function of the sliding quantity (S; S L; S TE) and a time derivative ( k̇ ( S,t); k̇ ( S L, t); k̇ ( S TE,t)) of the gain factor (k(S, t); k L (S L, t); k TE (S TE, t)) is a second function of the sliding quantity (S; S L; S TE; and the time derivative ( k̇ ( S, t); k̇ ( S L, t); k̇ ( S TE,t)) of the gain factor (k(S, t); k L (S L, t); k TE (S TE, t)) is negative in a first region (B 1) around the sliding manifold (S'), is zero in a second region (B 2) that surrounds the first region (B 1) and is positive in a third region (B 3) that surrounds the second region (B 2).