In this paper, we present a full spectro-polarimetric characterization of the Amplified Spontaneous Emission (ASE) emitted from a commercial, strained-bulk Semiconductor Optical Amplifier (SOA). A partly polarised, broadband noise source that draws from the same carrier reservoir as the amplified signal, ASE affects the state of polarisation of the overall outgoing signal of a SOA and its polarimetric behaviour is thus of interest. This study was carried out within the frame of the Stokes formalism, which not only allows a determination of the degree of polarisation (DOP) of ASE directly from its Stokes vector, but also gives access to a full, spectrally resolved characterization of its polarised fraction with respect to the applied bias current. Even when that fraction is small, its state of polarisation was shown to be strongly governed by the spectral dependence of the material gain upon polarisation. The same study was performed with a fully polarised signal injected into the SOA.