A scintillator based calorimeter with novel photo-detectors CALICE collaboration, Scintillator HCAL group The precision physics programme at a future linear collider requires a detector with unprecedented jet energy resolution. In the so-called particle flow approach, this critically depends on the spatial resolution of electromagnetic and hadronic sampling calorimeters and motivates very fine longitudinal and transverse segmentation. With novel photo-detectors, individual read-out of small scintillator tiles (of area 10cm**2 or less) becomes possible on a large scale. We explain the principle of operation and present the main characteristics of multi-pixel semiconductor photodiodes (the so-called Silicon photo-multiplier SiPM). The SiPM has 1024 pixels on an area of 1 mm**2 which operate independently in limited Geiger mode and provide a gain of about 10**6. The common signal is the sum of the pixel signals and an analogue measure of the light intensity. We report on the successful operation of a 108-channel prototype calorimeter in the DESY electron test beam. The design and expected performance of an 8000 channel prototype under construction for hadron test beams is also presented.