Hawaii Revised Statutes Division 1. Government § 236E-21

(a) If the amount paid with respect to any taxable transfer is less than the amount due under this chapter, the department shall assess the underpayment from the person responsible for payment, as follows:

(b) Amounts set forth on a duly filed and accepted federal return for valuations of property, the gross estate, federal taxable estate, and applicable exclusion amount shall be conclusive for purposes of this chapter, and the return required under this chapter shall use the same amounts as the corresponding amounts on the federal return; provided that with regard to a decedent who was in a valid civil union or recognized equivalent under the laws of the State, but that is not recognized by the Internal Revenue Code as a marriage for federal tax purposes, computations of the valuations of property, the gross estate, federal taxable estate, and applicable exclusion amount shall be made as if the civil union or recognized equivalent under the laws of the State were recognized as a marriage.

(c) If the amount paid with respect to any taxable transfer is more than the amount due under this chapter, the department shall refund the excess to the person entitled to the refund together with interest at the existing statutory rate of interest in the manner provided in section 231-23, as follows:

(d) As to all tax payments for which a refund or credit is not authorized by this section, including, without prejudice to the generality of the foregoing, cases of unconstitutionality, the remedies provided by appeal or by section 40-35 are exclusive.