Abstract Most circuit boards operate in environments that have the potential to be exposed to moisture, either in vapor or liquid form. Because low-cost circuit boards can readily absorb moisture, this can lead to performance issues, reliability issues, and even catastrophic failure. However, it is difficult to detect if moisture absorption has occurred before the circuit board suffers a complete failure. To alleviate this issue, a fringing field capacitor was implemented in printed circuit board (PCB) technology and used to detect the absorption of moisture in the circuit board through the accompanying increase in capacitance. Prototype sensors were fabricated and immersed for 42 d, demonstrating an increase in capacitance of between 14% and 29%. This sensor technology can easily be added to circuit board designs because they use the standard materials and fabrication processes used in commercial PCB construction.