The present invention is directed to the fabrication and use of phase-change material (PCM) membranes in microvalves for microfluidic systems. The microvalve may be fabricated by using a tissue-sectioning instrument to slice a thin membrane of PCM off of a block of PCM. The membrane may then be sandwiched between a plurality of microfluidic flow sections to act as a microvalve. At room temperature, the membrane may exist in a solid state to act as a zero-leakage seal and microvalve. Applying heat to the membrane may bring the membrane to a melting point, causing it to reach a liquid state. The microvalve in the liquid state may experience a surface tension effect by a material of the microfluidic flow sections, causing it to displace from a flow path and allow a fluid to pass from one microfluidic flow section to another.