Parallel operation of MOSFET can be done more easily as compared to thyristor because the resistance of MOSFET is increases with increase in temperature. MOSFET have the positive temperature coefficient. In positive temperature coefficient, the resistance increases with increase in temperature and in case of negative temperature coefficient resistance decrease with increase in temperature. Due to the positive temperature coefficient of MOSFET if we connect MOSFET in parallel and if the current in particular MOSFET increases then due to losses the temperature in that particular MOSFET will be increased. This increase in temperature will also increase the internal resistance of that particular MOSFET, therefore, the current in that particular MOSFET will also decrease this thing will balance the current in MOSFETs.
But in case of a thyristor which is a negative temperature coefficient device. So due to negative temperature coefficient, the resistance in the thyristor will decrease when the temperature of thyristor will increase this causes more current to flow due to low resistance.Hence the parallel operation of MOSFET can be done more easily as compared to the thyristor.