You would file a Form 7004 for Application for Automatic Extension of Time To File Certain Business Income Tax, Information, and Other Returns and you may find the form and instructions at: http://www.irs.gov/pub/irs-pdf/i... .If you have a valid 6-month Federal tax extension (IRS Form 7004), you will automatically receive a 6-month Delaware tax extension. In that case, do not submit a separate state extension request to the Delaware Division of Revenue. Just remember to attach a copy of Form 7004 to your Delaware return when itu2019s filed.In the State of Delaware you would file a Form 1100-EXT. A state tax extension only gives you more time to file, not more time to pay. You are still expected to pay your Delaware tax liability by the original deadline of your return (April 1). Failing to file and/or pay on time will result in penalties and interest charges.Use Form 1100-EXT (Corporation Income Tax Request for Extension) to apply for a Delaware tax extension. If you are making a payment with your extension, use Form 1100T-EXT (Corporate Request for Extension Voucher).Hope this information is helpful. Have a nice day!