Linear-mode Avalanche PhotoDiodes (APDs) can be fabricated in standard CMOS processes for obtaining high multiplication gains that allow to determine the number of incident photons with great precision. This idea can be exploited in several application domains, such as image sensors, optical communications and quantum information. In this work, we present a linear-mode APD fabricated in a 0.35 µm CMOS process and report its noise and gain characterization by means of two different experimental set-ups. Good matching is observed between the results obtained by means of the two different methods.