I turned on a light switch and noticed a few small sparks inside the
switch as I turned it on. No big deal, or so I thought.
After the lights were on for awhile I there was an 'electric burning'
smell. Sure enough the switch was hot to the touch.
Is it likely that the switch itself is bad and that replacing it will
solve the problem? (That I can easily do myself.)
Or could it be a more serious problem for which I should call an
electrician?
Thanks in advance for any help...
Try replacing the switch, making sure to use the screws to attach the
wires firmly to the new switch. Don't use the back stab wire inserts.
Also, if the wire insulation has become brittle, make sure to wrap it
well with good electrical tape, or if you have enough slack in the
wire, cut the wires back to where the insulation is pliable.

Also, before turning the power back on, check the wires in the
junction box that the light is attached to. Make sure they are in good
shape and attached firmly. If the insulation is brittle, cut back to
where it's pliable if slack permits, or wrap well with good electrical
tape.

Watch carefully. If the switch gets warm again, something else is
wrong, and you'll need to get it diagnosed.