A method of determining a value of a depth of a semiconductor junction of a substrate having a surface layer using a photomodulated optical reflectance measurement technique, the method comprising: - obtaining a substrate having at least a first region comprising the semiconductor junction, - obtaining a reference region (11', 11, 12) comprising a substrate having optical and semiconducting properties substantially equal to those of the substrate comprising the semiconductor junction, - performing at least one sequence of: i) selecting a set of measurement parameters for the photomodulated optical reflectance measurement, thereby selecting an offset between two spots on the substrate to which a pump laser beam and a probe laser beam are respectively focused so as to render both the plasma wave component in the layer and thermal component negligible relative to the plasma wave component in the substrate, ii) measuring from the at least a first region a first optical signal representative of the plasma wave component in the substrate at the semiconductor junction using the selected set of parameters, iii) measuring from the reference region a second optical signal using the selected set of parameters, iv) determining the ratio of the first optical signal to the second optical signal, and thereafter extracting by using the ratio, the depth of the semiconductor junction. - obtaining a substrate having at least a first region comprising the semiconductor junction, - obtaining a reference region (11', 11, 12) comprising a substrate having optical and semiconducting properties substantially equal to those of the substrate comprising the semiconductor junction, - performing at least one sequence of: i) selecting a set of measurement parameters for the photomodulated optical reflectance measurement, thereby selecting an offset between two spots on the substrate to which a pump laser beam and a probe laser beam are respectively focused so as to render both the plasma wave component in the layer and thermal component negligible relative to the plasma wave component in the substrate, ii) measuring from the at least a first region a first optical signal representative of the plasma wave component in the substrate at the semiconductor junction using the selected set of parameters, iii) measuring from the reference region a second optical signal using the selected set of parameters, iv) determining the ratio of the first optical signal to the second optical signal, and thereafter extracting by using the ratio, the depth of the semiconductor junction. i) selecting a set of measurement parameters for the photomodulated optical reflectance measurement, thereby selecting an offset between two spots on the substrate to which a pump laser beam and a probe laser beam are respectively focused so as to render both the plasma wave component in the layer and thermal component negligible relative to the plasma wave component in the substrate, ii) measuring from the at least a first region a first optical signal representative of the plasma wave component in the substrate at the semiconductor junction using the selected set of parameters, iii) measuring from the reference region a second optical signal using the selected set of parameters, iv) determining the ratio of the first optical signal to the second optical signal, and thereafter extracting by using the ratio, the depth of the semiconductor junction.