Background: Electrical conductivity, photoconductivity, voltage-controlled negative resistance and thermal properties of copolymers of 2-acrylamido-2-methyl-1-propanesulfonic acid and maleic acid were investigated in order to obtain new organic semiconductors. Results: The room temperature conductivity of three different copolymers was found to be in the range 1.28 × 10-8 - 1.20 × 10-7 S cm-1. The dark- and photo-current-voltage characteristics indicate that the copolymers exhibit voltage-controlled differential negative resistance behaviour. The electrical conductivity of the polymers increases by photo-illumination, suggesting that the polymers exhibit photoconductivity. The width of the exponential tail in the forbidden band gap of the three polymers was determined via the transient photocurrent technique and E0 values were in the range 34.4-36.49 meV. Conclusion: The results suggest that the copolymers could be used as organic semiconductor materials. © 2007 Society of Chemical Industry.