Texas Code of Criminal Procedure - CRIM P Art. § 19A.201. Grand Jury Impaneled

(a) When at least 16 qualified grand jurors are found to be present, the court shall select 12 fair and impartial persons as grand jurors and 4 additional persons as alternate grand jurors to serve on disqualification or unavailability of a grand juror during the term of the grand jury. The grand jurors and the alternate grand jurors must be randomly selected from a fair cross section of the population of the area served by the court.

(b) The court shall impanel the grand jurors and alternate grand jurors, unless a challenge is made to the array or to a particular person presented to serve as a grand juror or an alternate grand juror.

(c) A grand juror is considered to be impaneled after the grand juror's qualifications have been tested and the grand juror has been sworn.