In Jain Dharma, Siddha Kshetra means the place where liberated souls, called Siddhas, reside forever after attaining moksha.

What is Siddha Kshetra?

• It is not a physical worldly place like a city, mountain, or planet.
• It is the realm of liberation.
• Once a soul becomes completely free from karma, it rises to Siddhashila and stays there eternally as a Siddha.

Where is it in the universe?

According to Jain cosmology:

• The universe is called Lokākāśa.
• At the very top of the universe is Siddhashila.
• Siddha Kshetra is identified with this uppermost region of the loka.
• It is above the realms of humans, devas, and all other beings, and below the alokākāśa, which is empty space beyond the universe.

Important points

• Only liberated souls can exist there.
• Siddhas have no body, no suffering, no birth, no death, and no karma.
• They remain in pure consciousness, infinite knowledge, infinite vision, infinite bliss, and infinite energy.

In simple words

If you imagine the Jain universe vertically:

• Middle region: where humans live
• Lower regions: hells
• Upper regions: heavens
• Topmost point of the universe: Siddha Kshetra / Siddhashila

So, Siddha Kshetra is at the very top of the Jain universe, in the highest part of Lokākāśa.

If you want, I can also explain this with a simple Jain cosmology diagram in text form.