The relatively new field of stem cell biology is hampered by a lack of sufficient means to accurately determine the phenotype of cells. Cell-type-specific markers, such as cell surface proteins used for flow cytometry or fluorescence-activated cell sorting, are limited and often recognize multiple members of a stem cell lineage. We sought to develop a complementary approach that would be less dependent on the identification of particular markers for the subpopulations of cells and would instead measure their overall character. We tested whether a microfluidic system using dielectrophoresis (DEP), which induces a frequency-dependent dipole in cells, would be useful for characterizing stem cells and their differentiated progeny. We found that populations of mouse neural stem/precursor cells (NSPCs), differentiated neurons, and differentiated astrocytes had different dielectric properties revealed by DEP. By isolating NSPCs from developmental ages at which they are more likely to generate neurons, or astrocytes, we were able to show that a shift in dielectric property reflecting their fate bias precedes detectable marker expression in these cells and identifies specific progenitor populations. In addition, experimental data and mathematical modeling suggest that DEP curve parameters can indicate cell heterogeneity in mixed cultures. These findings provide evidence for a whole cell property that reflects stem cell fate bias and establish DEP as a tool with unique capabilities for interrogating, characterizing, and sorting stem cells.