A vertical rapid thermal processing (RTP) system (10) is provided, comprising a vertical process chamber (20) extending along a longitudinal axis (X), and a movable platform (32) disposed within the process chamber and having a support surface upon which one or more substrates such as semiconductor wafers (W) may be mounted for processing. A temperature control subsystem (56, 58, 60) establishes a continuous temperature gradient within the vertical process chamber along the longitudinal axis. The temperature control subsystem comprises a plurality of chamber sidewall heating elements (24) located at different vertical positions along the longitudinal axis. Each of the plurality of heating elements is controlled independently of the other of the plurality of heating elements. The plurality of longitudinally oriented heating elements provides an active sidewall heating mechanism which results in a consistent and continuous temperature gradient within the chamber, independent of the position of the wafer within the chamber or the number of wafers which have been processed.