Emission of ortho-positronium (o-Ps) from the surface of hydrogen-silsesquioxane (HSSQ) low-dielectric constant (low-k) films was studied with a newly developed Ps time-of-flight (TOF) measurement system. Clear TOF peaks were observed from a high porosity film (K131), indicating its higher open porosity in comparison with the other film (YK48) with less porosity. When the incident positron energy was raised from 0.5 to 4.0 keV, o-Ps emission energy for the former film was decreased from 1.1 to 0.07 eV. This is attributed to the increased o-Ps traveling distance inside an open pore. The presence of clear TOF peaks at high incident energies suggests that the open pores in K131 are well interconnected.