How bad a gap is in your resume depends on how you explain the gap. For example, if it’s clear in your resume that you spent six months out of the workplace taking a class to improve your professional skills, then a gap in your resume isn’t bad. You can even list the skills you learned in that class on your resume.
If the reason behind the gap in your resume isn’t clear, explain this period of unemployment in your cover letter. For instance, if you were laid off, explain that your company restructured. If you took time off to be a stay-at-home parent, state this clearly.