The present disclosure provides apparatus and methods for monitoring and controlling filaments used in hotwire semiconductor processing and for monitoring integrity of filaments in a hotwire processing chamber. Embodiments of this disclosure may use real time voltage and current feedback signals provided by the power supply, known attributes, for example resistivity, of filament, filament geometries, for example diameter and length, and filament assembly configurations as input, to derive filament temperature in real time. Embodiments of the present disclosure are capable of continuously derive accurate temperatures of the filament assembly in a hotwire processing chamber after the filament assembly has changed geometries due to normal usage by using the measured cold resistance of the wire periodically before the process starts.