Determining the very nature of an interface within a sliding contact is a central question in tribology. Contacts between asperities, normal and shear stresses and resulting real contact area are important characteristics governing friction losses but also wear. Despite the fundamental nature of these quantities, being able to experimentally and in-situ measure them is still a real challenge. This is even truer as far as extreme contact conditions are concerned, i.e. operating under high temperatures and/or contact pressures and/or sliding velocities. This work presents the development of a method for in-operando contact monitoring of a sliding contact. Based on an ultrasonic array of 32 elements, this approach uses wave propagation to assess the contact area and wear between two metallic materials. Each element of the probe is individually pulsed with a given sequence to construct a picture of the contact zone based on the reflected signals. A numerical model is first developed to study the propagation of the ultrasonic waves through a friction pin and its interaction with the contact interface. The influence of contact stresses and contact size on the ultrasonic signals is investigated in order to establish a method for online estimating the contact area. The experimental set-up is then described with the integration of an ultrasonic array on an open tribometer. A multi-channel pulser receiver is employed to control the probe while a dedicated software is used for processing the signals and monitoring in real time the data. Finally, an experimental campaign is performed with a cemented carbide pin sliding on a AISI 1045 steel to validate the methodology. •This campaign has explored ultrasonic reflectometry results as well as time of flight analysis WCCo rubbing against AISI1045.•The systems showed a different reaction between the two sliding conditions while giving a good repeatability.•In the case of dry sliding contact, the US signal is mostly sensitive to the geometrical modification of the rubbing pin end.•The heat flow has a secondary effect and give information of the thermal properties during sliding.•An thermal diffusion appears in the pins when it is leaving the contact and can be monitored with TOF analysis.•This paper also shown a deep correlation between geometry and thermal loads which is hard to decorelate.•This technology showed that the US technology is capable of monitoring the wear on metallic materials on a scale of 0–60 μm.