problem with discharging circuit

A schematic would be useful. Your description of the problem is not very clear (to me anyway).

Yes, there are a host of semiconductors that probably can be used for your application. It appears as if you are looking for a simple switching device? Again, a schematic would help clarify what exactly it is you are attempting to do. Then someone would be able to properly assist you.

I guess you wish to build a resistance welding machine. or something like it. or a flash circuit to touch lmp etc.

you can use a transistor or a thyristor to finish the task.

I know that there are many solutions to this problem, but why not try a simple resistor across your capacitor? If you do not want the resistor connected while it is operating, why not set that operation up using the on/off switch for the unit? It keeps things simple.

Either solution will work, although the semiconductor switch can better handle the arcing issue that will occur when you close the contacts of the mechanical relay or contactor, although it really is going to depend on how much stored charge you are working with. Do you know how many micro-Farads (uF) of storage you have? Is it for a camera or Xenon flash tube, coil gun, discharge welder, etc.

As you are asking a very simple electrical question, BE AWARE THAT CAPACITORS HAVE THE ABILITY TO STORE A LETHAL CHARGE AND CAN KILL YOU AS EASILY AS STICKING YOUR FINGERS IN THE SOCKET OUTLETS OF YOUR HOUSE!!

Please provide more information on your project and the size of capacitors you are planning to use.