Membrane-electrode assemblies (MEAs) are emerging cell configurations for many electrochemical energy conversions, such as water and CO2 electrolysis, due to their minimized ohmic losses because of the absence of electrolyte between electrode and membrane. The limited availability of electrolyte renders drastic deviation of electrode and membrane behaviour from those operated under flow-cell or H-cell configurations. However, significant challenges remain in accurately diagnosing electrodes or membrane MEAs due to their compact cell design that prevent straightforward placement of bulky reference electrodes into the MEAs. Despite recent progress in developing pseudo-reference electrodes for MEA diagnosis, the recent techniques suffered from significant voltage drifts and issues associated with detecting active area from the non-active regions. In this work, we address this critical challenge by developing ultrathin reference electrodes and embedment configurations to allow accurate measurement of voltages across the MEAs.