Why do the bottoms of my biscuits burn?

Thank you all for your excellent answers. I doubled the baking sheets, pre-heated for longer than usual, baked in the upper third of the oven, and used a silpat mat. Perfect golden bottoms.

All the above...plus I recommend a 'airbake' pan. It's double hulled with a air gap between the layers so it's a bit insulated from the direct radiant heat of an electric range.

Double up on your pan, and move to the top rack of your oven, away from the heat element. Also, have you had your oven calibrated? It may be burning hot.

The first thing to try, if you haven't already, is baking them on a higher oven rack. If that doesn't fix the problem, look at the thickness and material of your baking sheet. A thin or dark-colored baking sheet produces browner bottoms than a thicker, lighter colored one. If you have two baking sheets of identical size, try nesting them together to slow down the transfer of heat to the bottoms of the biscuits.

Are you pre-heating your oven?
Also, if they're in a lower oven shelf, the direct heat will cause this