Short channel effects have been investigated in n-channel polysilicon thin film transistors. Transconductance degradation has been observed when reducing the channel length L and this effect has been explained with the presence of a parasitic resistance related to residual implant damage. Threshold voltage slighlty decreases for channel length around L=1 mu m and simulations confirm that the roll-off of the threshold voltage is expected for L<1 mu m. In the output characteristics a stronger kink effect has been observed at short L which, from a comprehensive analysis of the current components, can be attributed to an enhanced parasitic bipolar transistor action. (C) 2005 Elsevier B.V All rights reserved.