Tamper-proof electronic packages and fabrication methods are provided including an enclosure enclosing, at least in part, at least one electronic component within a secure volume, a two-phase dielectric fluid within the secure volume, and a tamper-respondent detector. The tamper-respondent detector monitors, at least in part, temperature and pressure of the two-phase dielectric fluid. In operation, the two-phase dielectric fluid deviates from an established saturation line of the two-phase dielectric fluid within the secure volume with an intrusion event into the secure volume, and the tamper-respondent detector detects, from the monitoring of the temperature and pressure of the two-phase dielectric fluid, the deviation from the established saturation line, and thereby occurrence of the intrusion event.