Talking slightly off topic here, but you can parallel MOSFETs if you are driving them hard on (like in a switched mode power supply). If you are driving them in their Ohmic region (between fully off and fully on) then they do not share current very well. Differences in VGS threshold alone can ensure that one FET takes all the current while the other is nearly off. Also, the tempco is only positive when in the fully enhanced region enabling a level of thermal regulation, but not so in the Ohmic region.