Black phosphorus (BP) has been proposed as a future optoelectronic material owing to its direct bandgap with excellent electrical performances. However, oxygen (O-2) and water (H2O) molecules in an ambient condition can create undesired bubbles on the surface of the BP, resulting in hampering its excellent intrinsic properties. Here, we report the electrical degradation pattern of a mechanically exfoliated BP field-effect transistor (FET) in terms of the channel and contact, separately. Various electrical parameters such as the threshold voltage (V-TH), carrier mobility (mu), contact resistance (R-CT) and channel resistance (R-CH) are estimated by the Y function method (YFM) with respect to time (up to 2000 min). It is found that R-CT reduces and then, increases with time; whereas, the behavior of R-CH is vice versa in ambient conditions. We attribute these effects to oxygen doping at the contact and the surface oxidation effects on the surface of the BP, respectively. (C) 2017 Published by Elsevier B.V.